The main causes of a two-wheeled vehicle accident are speeding and an inefficient braking force. Also during ordinary driving, if sudden braking due to an emergency situation is applied to a rear wheel, a decreased coefficient of friction between a road surface and a tire increases the braking distance to potentially cause an accident. When a front wheel is locked, the two-wheeled vehicle, unlike a four-wheeled vehicle, loses balance to cause an overturn, which results in an uncontrollable situation due to a loss of function as a steering and braking device, potentially leading to a serious accident.
FIG. 5 is a graph for describing a brake hydraulic pressure. In the graph, A shows a conventional brake system (non-ABS) of a two-wheeled vehicle; C shows a lock point; D is a hydraulic pressure set value pursued in the present invention and shows the maximum value of the brake pressure that is shut off to prevent skidding on a normal road surface; and B shows a variation in hydraulic pressure at which anti-lock and locked states are switched in an electronic antilock brake system (ABS).
In a conventional two-wheeled vehicle brake system (non-ABS), choosing a rear-wheel brake for sudden braking applies a braking force insufficient for adequately for shortening the braking distance due to a decreased friction force between the road surface and the tire, and choosing a front-wheel brake increases the friction force between the road surface and the tire to make the braking force increase, but if the front wheel is locked beyond the lock point B, a vehicle body will become lain on the ground due to a biased load (slip toward lateral road surface within 90 degrees to left or right), which causes loss of function as a steering and braking device, leading to an uncontrollable situation and a potentially serious accident. That is, the area beyond the lock point B in A falls under the skid generating area due to unnecessary excess hydraulic pressure that is hazardous to a rider.
An electronic ABS has clear advantages of excellent operation on a bad road surface as well as a shortened braking distance, but has two disadvantages as follows.
First, it is difficult to mount the electronic ABS unless it is mounted as an option prior to delivering a new two-wheeled vehicle. More specifically, to mount an electronic ABS on a two-wheeled vehicle that has already been delivered, the vehicle body of the two-wheeled vehicle should be remodeled, so it is almost impossible to mount the electronic ABS in view of time and cost. At present, some products with high-class specifications are delivered with the ABS not optional but built-in. It is difficult to estimate the unit factory price of ABS, but is estimated roughly at $1,000.00, and some brands cost more. Thus, it becomes contradictory that a price higher than the price of the motorcycle itself should be paid to mount an ABS on a small low-class motorcycle.
Second, sudden braking in a quick-turn cornering causes slipping due to ABS action and may lead to a serious accident because of an overturn of the motorcycle. In other words, it is commonsense that a quick turn during sudden braking can be made only within the limit of friction force between the road surface and the tire. But even within the limit of friction force, if the motorcycle slips within a very short time with an inertia and centrifugal force applied thereto, slipping that has already started will continue. At this time, even if a hydraulic pressure is reduced with a command of unlocking what was locked from an ECU for an electronic ABS, it is impossible for the motorcycle, for which the slip and overturn has already started, to stop the overturn with the slip suspended and stand up again to drive upright no matter how quickly and greatly the decompression of a brake is provided.
To solve such problems, the applicant filed an application to disclose Korean Patent Application No. 10-2000-0011021 (a mechanical automatic hydraulic control device for an antilock brake system). The above invention deals with the response of the brake system started by the action of a brake pedal or brake lever during a brake action, so that when stopping or reducing the velocity of the vehicle or machine, less than the minimum value of hydraulic pressure for the wheel to be locked is passed in a vehicle in the direction of a wheel cylinder or caliper, and more than the locked pressure is automatically shut off, and in the case of machinery, damage or deformation due to a sudden stop is prevented, so unlike an ordinary brake system or ABS brake system, the hydraulic pressure is increased by stepping on the brake pedal or pulling the brake lever, and the increase of hydraulic pressure is stopped in a state proximate to the lock point, and in such a state the wheel is does not slip and rotates at an optimum speed along with deceleration. Therefore, it has an advantage that the turning of the vehicle body by biased weight of the vehicle body or the skid condition by slipping is minimized during braking.
However, the invention of Korean Patent Application No. 10-2000-0011021 has a problem that the brake function may be lost momentarily due to the breakaway of a control bolt because of an external shock or vibration due to long-term repetitive use.